Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

Above critical temperature

2. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 9

1: 3

1: 1

3. Most thermostatic expansion valves are set for a superheat of

5°C

10°C

20°C

15°C

4. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

5. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

6. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Positive

Negative

7. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Piston type reciprocating

Axial

8. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

High risibility with oil

Low boiling point

Large latent heat

9. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.4

0.6

0.67

10. Which of the following cycles uses air as the refrigerant?

Ericson

Carnot

Bell Coleman

Stirling

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11. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

12. Rating of a domestic refrigerator is of the order of

0.1 ton

40 tons

5 tons

10 tons

13. The freezing point of sulphur dioxide is

-135.8°C

-56.6°C

-77.7°C

-75.2°C

14. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

2 bar

30 bar

8 bar

15. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

16. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

17. In a lithium bromide absorption refrigeration system

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

18. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

19. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

Water will evaporate

20. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

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21. For obtaining high COP, the pressure range of compressor should be

Low

Any value

Optimum

High

22. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

23. The bank of tubes at the back of domestic refrigerator is

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

Condenser tubes

24. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

25. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

26. The curved lines on a psychrometric chart indicates

Dew point temperature

Wet bulb temperature

Relative humidity

Dry bulb temperature

27. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

28. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

3.33

4.33

29. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser

Absorber

Condenser, absorber and separator (rectifier)

30. The capillary tube, as an expansion device, is used in

Water coolers

Domestic refrigerators

Room air conditioners

All of these

Page 4 of 4

31. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Equal to unity

Always more than unity

Any one of the above

32. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

33. The boiling point of ammonia is

-33.3°C

-10.5°C

-77.7°C

-30°C

34. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

35. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

36. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Three heat exchangers

Four heat exchangers

37. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

Collect vapours

38. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

39. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Freon

Brine

40. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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